Early vaccination and protection of Atlantic cod (Gadus morhua L.) juveniles against classical vibriosis

The effect of vaccinating Atlantic cod (Gadus morhua L.) juveniles weighing from 1 to 20 g with a commercial vibriosis vaccine (ALPHA MARINE™ Vibrio, PHARMAQ AS) was determined by bath challenge with Vibrio anguillarum serotype O2b. Bath vaccination of cod juveniles of 1 g resulted in a poor protection when challenged 6 weeks later (RPS < 47%). In addition, the durability of the protection was poor since challenge 14 weeks post vaccination resulted in RPS < 36%. Apparently, the cod juveniles need to reach a certain size at the time of vaccination in order to obtain a good protection. A significant increase in protection was demonstrated 7 weeks post dip vaccination at 2.2 g (RPS > 75) compared to 1.7 g (RPS < 54). Moreover, dip vaccination at 5 g elicited a very good and long-lasting protection for at least 28 weeks post vaccination (RPS > 76), that was comparable to the protection obtained 17 weeks post dip or i.p. vaccination at 20 g (RPS > 74).